Start Plants Indoors Before the Last Frost
The main difference between summer and winter squash is that winter squashes have hard, thick rinds that will help them store for long periods of time. In cooler regions, you can start plants indoors three weeks before the last frost date. You don't want to start plants any earlier than this because older plants sometimes will not transplant well.
To start the winter squash indoors, put two seeds, 1" deep into 4" peat pots and water them until the soil was moist (Image 1). For best germination, you need to maintain the seeds at a constant temperature of 65 to 85 degrees Fahrenheit. Using grow lights is the best way to maintain a constant temperature.
Once the seedlings reach 2" tall, use scissors to thin the plants to one per pot. Also, before you plant the seedlings outdoors, harden off the seedlings. Hardening off means to gradually acclimate the seedlings to the outdoors. Place seedlings outside during the day under shrubs or trees when the temperatures are above 40 degrees Fahrenheit. Don't forget to bring the seedlings in at night and after five to seven days of hardening off, they will be ready for transplanting outside (Image 2).